Series capacitor protective device



Aug. 10, 1954 A. VAN RYAN 2,636,233

SERIES CAPACITOR PROTECTIVE DEVICE Original Filed March 30, 1950 51 ,424GAP @9564 OS/N6 i CAPCO/T EIPEAKATQ CAPAC/ 7 0/2 INVENTOR.

Patented Aug. 10, 1954 SERIES CAPACITOR PROTECTIVE DEVICE Anthony VanRyan, South Milwaukee, Wis., assignor to McGraw Electric Company,Milwaukee, Wis., a corporation of Delaware Original application March30, 1950, Serial No.

152,801, now Patent No. 2,656,490, dated October 20, 1953. Divided andthis application December 30, 1950, Serial No. 203,699

2 Claims. 1

This invention relates to a series capacitor protective device.

This application is a division of my prior application Serial No.152,801, filed March 30, 1950, now Patent 2,656,490, Oct. 20, 1953, forSeries Capacitor Protective Device and System, assigned to the sameassignee as the present appllcation.

Up to the present time, series capacitors have not been widely usedbecause of the difliculty and great expense of protecting them fromexcessive currents upon occurrence of faults and from over-voltage dueto surges. However, it is desirable to use series capacitors for voltagecorrection in distribution lines as they can be cheaply constructed anddo not have to withstand the full line voltage under ordinary op eratingconditions.

This invention is designed to provide a system of voltage correctionwhich employs series capacitors and which provides for the protection ofthe series capacitors in the event of a surge, fault, or other abnormalcondition.

Specific objects of this invention are to provide a series capacitorprotective device which is so constructed that it coacts with arepeating, lock-out circuit interrupter, and which is so made that itwill restore itself to its normal condition when the power line is againunder normal conditions.

A further object of this invention is to provide a construction which isvery simple and. may be easily installed in a polyphase or single phasepower line, for instance, with a minimum of change and which providesmaximum protection for the series capacitor.

An embodiment of the invention is shown in the accompanying drawings, inwhich:

The single figure is a diagrammatic view showing the device applied toone phase or line of a polyphase system, the remaining devices beingsimilar but being omitted for the sake of simplicity.

Referring to the drawings, it will be seen that a polyphase line hasbeen indicated by the reference character I. In each phase of this linea repeating lock-out circuit breaker 2 is installed, one only havingbeen shown in the diagram. The series capacitor is indicated by thereference character 3 and is bridged by means of a spark gap 4 which hasa relatively low breakdown voltage as compared with that of the normalvoltage between phases. It has a breakdown voltage somewhat below thesafe working voltage of the series capacitor 3, so that it is thusarranged to spark-over and provide a bypass whenever a voltage isproduced between the terminals of the series capacitor above thebreakdown voltage of the spark gap.

In conjunction with the spark gap, an automatic, magnetically operated,by-passing protective device 5 is employed. This device may comprise acasing 6 within which is mounted an actuating or energizing coil 1 whichnormally holds a magnetic plunger 8 in an elevated position duringcurrent flow. This coil 7 is connected in parallel with the spark gap 4and the series capacitor 3. The plunger 8 carries or actuates a movablecontact 9 which is arranged to bridge stationary contacts 10 when itdrops down. However, the plunger 8 and movable contact 9 are springsupported by means of a spring 8, and are arranged so that the movablecontact 9 is held just out of contact with the stationary contacts Iteven when the coil 1 is deenergized, as shown in dotted lines. Thestationary contacts H) are preferably somewhat resilient Or resilientlymounted and are connected across the series capacitor 3 and the sparkgap 4. When the coil 1 is energized, the plunger 8 and movable contact 9are held in an elevated position as shown in full lines. When the coil lis suddenly deenergized, the plunger 8 and movable contact 9 willsuddenly drop down and the movable contact 9 will momentarily engage thestationary contacts 10 and bridge the spark gap 4.

The spring 8' alone will hold the movable contact 9 slightly out ofengagement with the stationary contacts I E! as shown in dotted lines.Current flow through the line will cause a further elevation of thecontact 9 and plunger 8, and a current flow equivalent to the minimumtrip current of the reclosing lock-out circuit breaker will cause amaximum elevation of the plunger 8 and contact 9. A further increase incurrent flow through the capacitor will cause a potential to appearacross its terminals sufficient to cause flash-over of the spark gap 4.Also any potential surges on the line equal to or in excess of thisvoltage will cause a flash-over of the spark gap 4. The spark gapprovides a shunt or by-pass around the coil 7 which, when the gap sparksover, will cause the plunger 8 and movable contact 9 to drop downwardlypast the dotted line position due to the inertia of said plunger 3 andmovable contact 9 and thereby temporarily bridge the stationary contactsIn, thus shorting out the spark gap and thereby extinguishing the sparkat the spark gap. The

movable contact 9 is returned to the position shown in the dotted lines,or to any position corresponding to the current flowing through thecoil.

If the condition causing the aforementioned action is temporary, theplunger 8 and contact 9 will return to switch open position. However, inthe event of a permanent fault, the movable contact 9 will repeatedlyengage stationary contacts l until the repeating lock-out, circuitbreaker will finally lock out.

It is to be distinctly understood that between the imaginary lines II,II, a plurality of these units as hereinabove described are provided,one set for each power line. For the sake of simplicity, however, onlyone set of units has been illustrated.

It will be seen that a very simple type of series capacitor withprotective means therefor has been provided. Further, it will be seenthat the series capacitors may be installed for voltage correction indistribution systems with assurance of full protection for thecapacitors.

It is obvious that either individual reclosing lockout circuit breakersindicated by the reference character 2, or a polyphase, lock-out circuitbreaker, may be'used without departing from the spirit of thisinvention. It is to be understood that the circuit breaker 2, which maybe called a back-up circuit breaker, must be coordinated with thecapacitor in such a way that its minimum trip current will be equal tothe maximum current that the capacitor can continuously carry withoutproducing a destructive potential across the capacitor.

The tank 6 may be oil or gas filled and the specific mechanicalconstruction of the device may be varied as required, provided, however,that the switch means is normally held open under no load and under loadconditions and is arranged to close temporarily under abnormalconditions as described.

It will be seen that the device is relatively simple and that it willprovide adequate protection for a series capacitor.

It is to be understood that no attempt has been made to show details ofthe specific manner in which the protective device or the spark gap 4 isconstructed. It is to be understood, however, that all of the live partsare insulated from other portions of the apparatus.

It will be seen further that the electromagnetically controlled switchmeans is responsive to the voltage across the capacitor. Further it willbe seen that such electromagnetically controlled switch means is, initself, controlled by the spark gap, for so long as the spark gap isintact, the switch means remains open, but as soon as the spark gapbreaks down, the switch means temporarily closes and extingulshes thespark.

Although this invention has been described in considerable detail, it isto be understood that such description is intended as illustrativerather than limiting, as the invention may be variously embodied and isto be interpreted as claimed.

I claim:

1. A protective device comprising switch means, electromagnetic meanscontrolling said switch means and including an armature for operatingsaid switch means, a coil for moving said armature from a firstswitch-open position to a second switch-open position upon energizationof said coil, means biasing said switch means towards switch-closedposition when held in said second position, said switch means being heldin said second position at all times when said coil is energized, andspring means for holding said switch means in said first position whenthere is no current flow through said coil, said switch means andarmature having a predetermined amount of inertia to cause said switchmeans to temporarily close when said coil is suddenly deenergized aftersaid coil has been energized.

2. A protective device comprising switch means consisting of a movablecontact and resilient stationary contacts, electromagnetic meanscontrolling said switch means and including an armature for operatingsaid switch means, a coil for moving said armature from a firstswitchopen position to a second switch-open position upon energizationof said coil, means biasing said switch means towards switch-closedposition when held in said second position, said switch means being heldin said second position at all times when said coil is energized, andspring means for holding said switch means in said first position whenthere is no current flow through said coil, said switch means andarmature having a predetermined amount of inertia to cause said switchmeans to temporarily close when said coil is suddenly deenergized aftersaid coil has been energized.

References Cited. in the file of this patent UNITED STATES PATENTSNumber Name Date 50 Richardson Nov. 1893 1,1 5,465 Stone July 28, 19141,214,779 Hall Feb. 6, 1917 FOREIGN PATENTS Number Country Date 149,673Great Britain Apr. 28, 1921 436,073 Germany Oct. 23, 1926

